Programmable Anisotropic Terahertz Permittivity via High‐Aspect‐Ratio 3D‐Printed Dielectric Mesh Networks

We present a 3D-printed anisotropic dielectric with programmable terahertz permittivity. The design embeds a mesh network of high-aspect-ratio void channels within a bulk substrate. The anisotropic electromagnetic response, which depends on the orientation of the void channels relative to terahertz polarization, was systematically evaluated against various Effective Medium Theories. The Wiener Upper Bound describes the case where channels are oriented parallel to the terahertz polarization, while the Lichtenecker-Roth model, with a structural parameter of 0.33, describes the perpendicular case. To validate our approach, mesh substrates with infill densities of 25%, 50%, and 75% were fabricated using a state-of-the-art two-photon polymerization direct laser writing system, Nanoscribe Photonic Professional GT2, yielding void channels with an aspect ratio of 120. Characterization via terahertz time-domain spectroscopy confirmed that varying the infill density modulates the effective permittivity over the frequency range from 0.4 to 1.0 THz. The measured permittivity spans 1.52 (25% infill) to 2.76 (bulk solid), with a dielectric anisotropy of 0.15 at 0.5 THz. These experimental results agree with the simulations to within 3% for the substrates with 50% and 75% infill densities, establishing a reliable framework for future applications.